1. Field of the Invention
The present invention relates to a lens meter for measuring optical characteristics of a subject lens to be measured.
2. Description of Related Art
Conventionally, there is proposed a lens meter for measuring optical characteristics of a subject lens to be measured, which collimates a measurement light bundle emitted from a light source for measurement by a collimator lens to project the measurement light bundle onto the subject lens, photo-receives the measurement light bundle passing through the subject lens on a two-dimensional photodetector via at least three pinholes (openings) and convergent lenses arranged respectively therein, and detects positions of pinhole images (refer to Japanese Patent Application Unexamined Publication No. Hei 11-125581).
Further, proposed is a lens meter in which a diffraction lens array is arranged as convergent lenses for pinholes in order to prevent an inaccurate measurement result brought by local disturbance in a wavefront of the measurement light bundle or deformation of pinhole images resulting from a scratch or soil on a subject lens to be measured (HORI, Nobuo et al., “Application of a Diffraction Optical Element to Measurements”, OPTICAL ALLIANCE, Japan Industrial Publishing Co., Ltd., Tokyo, (Nov., 1998), PP.36-39).
However, the diffraction lens array arranged for the pinholes is hard to work and high in cost. Further, when there is a big scratch or soil on the subject lens, there may be cases where an inaccurate measurement result cannot be prevented.